Characterization of buffy coat-derived granulocytes for clinical use: a comparison with granulocyte colony-stimulating factor/dexamethasone-pretreated donor-derived products.

BACKGROUND AND OBJECTIVES: Buffy coat-derived granulocytes have been described as an alternative to the apheresis product from donors pretreated with dexamethasone and granulocyte colony-stimulating factor (G-CSF). The latter is - dependent on the local and national settings - obtained following a demanding and time-consuming procedure, which is undesirable in critically ill septic patients. In contrast, buffy coat-derived products have a large volume and are often heavily contaminated with red cells and platelets. We developed a new pooled buffy coat-derived product with high purity and small volume, and performed a comprehensive functional characterization of these granulocytes. MATERIALS AND METHODS: We pooled ten buffy coats following the production of platelet concentrates. Saline 0·9% was added to decrease the viscosity and the product was split into plasma, red cells and a 'super' buffy coat. Functional data of the granulocytes were compared to those obtained with granulocytes from healthy controls and G-CSF/dexamethasone-pretreated donors. RESULTS: Buffy coat-derived granulocytes showed adhesion, chemotaxis, reactive oxygen species production, degranulation, NETosis and in vitro killing of Staphylococcus aureus, Escherichia coli and Aspergillus species comparable to control and G-CSF/dexamethasone-derived granulocytes. Candida killing was superior compared to G-CSF/dexamethasone-derived granulocytes. Immunophenotyping was normal; especially no signs of activation in the buffy coat-derived granulocytes were seen. Viability was reduced. Buffy coats are readily available in the regular blood production process and would take away the concerns around the apheresis product. CONCLUSION: The product described appears a promising alternative for transfusion purposes.

Regulation and kinetics of platelet-activating factor and leukotriene C4 synthesis by activated human basophils.

BACKGROUND: Allergic disease is the result of an interplay of many different cell types, including basophils and mast cells, in combination with various inflammatory lipid mediators, such as platelet-activating factor (PAF) and leukotrienes (LT). LTC4 synthesis by human basophils has been studied quite extensively. However, not much is known about the synthesis of PAF by human basophils. OBJECTIVE: In this study, we have made a comprehensive comparison between the kinetics of PAF and LTC4 synthesis, in highly purified basophils, activated with different stimuli or with combinations of stimuli. METHODS: Synthesis of PAF and LTC4 by human basophils was determined with commercially available assay kits. The basophils were activated with C5a, fMLP, PMA, allergen or anti-IgE, in the absence and presence of IL-3 and/or in combination with elevation of cytosolic free Ca2+ by the sarcoplasmic reticulum Ca2+-ATPase inhibitor thapsigargin. RESULTS: Most stimuli were found to induce both PAF and LTC4 synthesis. PAF synthesis and LTC4 release were enhanced by preincubation of the basophils with IL-3 or by elevation of cytosolic free Ca2+ by thapsigargin. Incubation of human basophils with IL-3 alone or thapsigargin alone did not result in detectable synthesis of PAF and LTC4, whereas the combination of the two resulted in high amounts of PAF and LTC4 synthesis. Depending on the stimulus used, LTC4 release was 5-100-fold higher than PAF synthesis. In addition, PAF, but not LTC4, was transiently detected, probably due to PAF degradation. LTC4 and PAF synthesis was strongly blocked by inhibitors of cytosolic phospholipase A2, indicating that this enzyme is involved in PAF and LTC4 synthesis by activated human basophils. CONCLUSION: This study provides a first comprehensive comparison of PAF and LTC4 synthesis in highly purified human basophils, stimulated with a variety of stimuli.

Interference of PR3-ANCA with the enzymatic activity of PR3: differences in patients during active disease or remission of Wegener's granulomatosis.

Anti-neutrophil cytoplasmic antibodies (ANCA) against proteinase 3 (PR3) are strongly associated with Wegener's granulomatosis (WG) and are thought to be involved in its pathogenesis. Levels of PR3-ANCA do not always correspond to clinical disease activity. To investigate the relationship between functional effects of PR3-ANCA and disease activity, we tested the effect of IgG samples from sera of 43 WG patients, taken during active disease or remission, for their capacity to interfere with the proteolytic activity of PR3. Furthermore, longitudinal sera of seven WG patients were included. The enzymatic activity of PR3 was determined (1) with casein or with a small synthetic substrate and (2) by complexation of PR3 with alpha1-antitrypsin (alpha1-AT). With a fixed concentration (100 microg/ml) of IgG, PR3-ANCA from patients during an active phase of WG had a higher inhibitory capacity towards the proteolytic activity of PR3 and complexation of PR3 with alpha1-AT than did PR3-ANCA from WG patients during remission. However, the number of PR3-ANCA units that gave 50% inhibition of the PR3 enzymatic activity and its complexation with alpha1-AT was lower for patients during remission than for patients during an active phase of WG, indicating a stronger inhibitory capacity at a molar base. In conclusion, PR3-ANCA from patients during remission had a relatively higher inhibitory capacity towards the enzymatic activity of PR3 than PR3-ANCA from patients during an active phase. This may indicate that during active disease the ANCA titre is increased, but the number of active ANCA molecules that recognize the enzyme-inhibiting epitopes is not increased.

The impact of platelet-activating factor (PAF)-like mediators on the functional activity of neutrophils: anti-inflammatory effects of human PAF-acetylhydrolase.

Platelet-activating factor (PAF) is a proinflammatory agent in infectious and inflammatory diseases, partly due to the activation of infiltrating phagocytes. PAF exerts its actions after binding to a monospecific PAF receptor (PAFR). The potent bioactivity is reflected by its ability to activate neutrophils at picomolar concentrations, as defined by changes in levels of intracellular Ca(2+) ([Ca(2+)](i)), and induction of chemotaxis and actin polymerization at nanomolar concentration. The role of PAF in neutrophil survival is, however, less well appreciated. In this study, the inhibitory effects of synthetic PAFR-antagonists on various neutrophil functions were compared with the effect of recombinant human plasma-derived PAF-acetylhydrolase (rPAF-AH), as an important enzyme for PAF degradation in blood and extracellular fluids. We found that endogenously produced PAF (-like) substances were involved in the spontaneous apoptosis of neutrophils. At concentrations of 8 microg/ml or higher than normal plasma levels, rPAF-AH prevented spontaneous neutrophil apoptosis (21 +/- 4% of surviving cells (mean +/- SD; control) versus 62 +/- 12% of surviving cells (mean +/- SD; rPAF-AH 20 microg/ml); P < 0.01), during overnight cultures of 15 h. This effect depended on intact enzymatic activity of rPAF-AH and was not due to the resulting product lyso-PAF. The anti-inflammatory activity of rPAF-AH toward neutrophils was substantiated by its inhibition of PAF-induced chemotaxis and changes in [Ca(2+)](i). In conclusion, the efficient and stable enzymatic activity of rPAF-AH over so many hours of coculture with neutrophils demonstrates the potential for its use in the many inflammatory processes in which PAF (-like) substances are believed to be involved.

Vasoactive side effects of intravenous immunoglobulin preparations in a rat model and their treatment with recombinant platelet-activating factor acetylhydrolase.

Previously, we observed in a rat model that intravenous administration of intramuscular immunoglobulin preparations induced a long-lasting hypotension, which appeared to be associated with the presence of IgG polymers and dimers in the preparations, but unrelated to complement activation. We found evidence that this hypotensive response is mediated by platelet-activating factor (PAF) produced by macrophages. In this study, we compared the vasoactive effects of 16 intravenous immunoglobulin (IVIG) products from 10 different manufacturers, in anesthetized rats. Eight of the IVIG preparations showed no hypotensive effects (less than 15% decrease), whereas the other 8 had relatively strong effects (15%-50% decrease). The hypotensive effects correlated with the IgG dimer content of the preparations. Pretreatment of the rats with recombinant PAF acetylhydrolase completely prevented the hypotensive reaction on IVIG infusion, and administration after the onset of hypotension resulted in normalization of the blood pressure. We also observed PAF production on in vitro incubation of human neutrophils with IVIG, which could be blocked by anti-Fcgamma receptor antibodies. This indicates that induction of PAF generation may also occur in a human system. Our findings support the hypothesis that the clinical side effects of IVIG in patients may be caused by macrophage and neutrophil activation through interaction of IgG dimers with Fcgamma receptors. Because phagocyte activation may also lead to the release of other inflammatory mediators, recombinant PAF acetylhydrolase (rPAF-AH) provides a useful tool to determine whether PAF plays a role in the clinical side effects of IVIG. If so, rPAF-AH can be used for the treatment of those adverse reactions. (Blood. 2000;95:1856-1861)

Influence of structurally different lipid emulsions on human neutrophil oxygen radical production.

BACKGROUND: The aim of this study was to evaluate immunomodulatory properties of lipid emulsions applied in parenteral nutrition by measuring neutrophil oxygen radical production (the 'respiratory burst') after lipid incubation. MATERIALS AND METHODS: Neutrophils, isolated from the blood of 10 healthy individuals, were incubated in medium or in lipid emulsions in a physiological concentration (2.5 mmol L-1) containing long-chain [Intralipid (LCT)], mixed medium and long-chain [Lipofundin (LCT/MCT)] or structured triglycerides (SL). After washing and stimulation with phorbol 12-myristate 13-acetate (PMA) or serum-treated zymosan (STZ) particles, the respiratory burst was evaluated by measuring maximum oxygen uptake, superoxide and hydrogen peroxide production rates and chemiluminescence. RESULTS: Unlike LCT and SL, LCT/MCT increased PMA- and STZ-induced oxygen uptake rate by 45% and 31% respectively (both P = 0.006 compared with medium) as well as superoxide (+56%, P = 0.006) and hydrogen peroxide (+14%, P = 0.04) production, within 5 min after stimulation. Increased LCT/MCT-mediated early respiratory burst was confirmed by decreased PMA- (-65%) and STZ-stimulated (-54%) chemiluminescence peak time (time after stimulation to peak) in combination with unchanged peak height (maximum rate of radical production). Late respiratory burst (within 2 h) of LCT/MCT, indicated by overall luminescence (overall radical production), remained unchanged (PMA) or decreased (STZ, P = 0.02). The addition of 2.5 mmol L-1 LCT/MCT or MCT emulsion to unstimulated neutrophils, in contrast to LCT and SL, resulted in significant luminescence. CONCLUSIONS: Early neutrophil respiratory burst is accelerated by the LCT/MCT emulsion Lipofundin, whereas LCT (Intralipid) and structured lipid emulsions exert no effect. MCT-containing emulsions, contrary to LCT and structured lipid emulsions, can induce oxygen radical production in unstimulated neutrophils.

Impaired leukocyte phagocytosis in patients undergoing hemihepatectomy for liver metastases.

Patients undergoing partial hepatectomy have an increased susceptibility to infection. To investigate whether this increased risk is related to impaired leukocyte function, we studied polymorphonuclear leukocyte (PMN) phagocytosis in patients undergoing a hemihepatectomy because of liver metastasis (LM, n = 11) and in patients undergoing major abdominal surgery because of abdominal malignancy (AM, n = 8). Eight healthy volunteers (HVs) served as controls. Leukocyte suspensions were incubated with fluorescein isothiocyanate-labeled Staphylococcus aureus, and phagocytosis was measured by flow cytometry. Preoperative PMN phagocytosis, in the presence of autologous plasma, was significantly less in patients with LM compared with patients with AM or HVs. This impaired phagocytosis was potentially restored in the presence of normal plasma. The decreased phagocytic capacity of PMNs from patients with LM was not related to levels of known plasma opsonins or phenotypic changes of PMNs. Rather, it was related to a deficiency of unidentified plasma factors. After surgery, the phagocytic capacity of PMNs of patients with AM decreased by approximately 30%, which correlated with decreasing levels of immunoglobulin G and C3. In conclusion, patients with LM had a decreased PMN phagocytic capacity before surgery. This impairment in phagocytosis disappeared 1 week after surgery. We propose that the presence of LM leads to a deficiency of factor(s) in the blood that impairs PMN phagocytic capacity.

Phospholipase D-derived phosphatidic acid is involved in the activation of the CD11b/CD18 integrin in human eosinophils.

Priming of human eosinophils is an essential event for the respiratory burst induced by serum-opsonized particles [serum-treated zymosan (STZ)]. In this study we have found that treatment of eosinophils with platelet-activating factor (PAF) leads to activation of phospholipase D. Inhibition of the formation of phospholipase D-derived products by ethanol resulted in about 90% inhibition of PAF-induced binding of fluorescent STZ particles to the cells, but only when ethanol was added to the cells before treatment with PAF. When ethanol was added after treatment with PAF, only a minor inhibition of the STZ binding and STZ-induced response was observed. These results indicate that phospholipase D-derived phosphatidic acid is involved in PAF priming, without having an effect on STZ stimulation. In the presence of propranolol, which inhibits phosphatidic acid-phosphatase activity, binding of STZ particles to human eosinophils induced by suboptimal concentrations of PAF was enhanced, indicating that phosphatidic acid and not diradylglyceride is the relevant molecule derived from phospholipase D activity. Addition of cell-permeant diC8-phosphatidic acid (DiC8-PA) to human eosinophils resulted in CD11b/CD18-dependent adhesion, both to STZ particles and fibronectin-coated wells, without significant upregulation of CD11b/CD18. The DiC8-PA-induced adhesion was not mediated via the fatty acid moiety, because other C8-lipids such as 1,2-diC8-phosphatidylcholine, 1-C8-monoacylglycerol or C8-ceramide were without effect. Activation of protein kinase C with PMA or 1,2-diC8-diacylglycerol did result in enhanced STZ binding. However, under these latter conditions upregulation of CD11b/CD18 was observed. Taken together, these results suggest that phospholipase D-derived PA is involved in changing the affinity of the CD11b/CD18 integrin for its ligands.

Human eosinophils express, relative to other circulating leukocytes, large amounts of secretory 14-kD phospholipase A2.

Human eosinophils perform several functions dependent on phospholipase A2 (PLA2) activity, most notably the synthesis of platelet-activating factor (PAF) and leukotriene C4 (LTC4). Several forms of PLA2 have been identified in mammalian cells. In the present study, the 14-kD, secretory form of PLA2 was detected in human eosinophils by immunocytochemical staining with the specific monoclonal antibody (MoAb) 4A1. In contrast, preparations of neutrophils, monocytes, lymphocytes, and basophils did not show detectable staining. With two MoAbs in a sandwich enzyme-linked immunosorbent assay (ELISA), large amounts of sPLA2 were detected in lysates of eosinophils, that were 20-fold to 100-fold higher than in the other circulating leukocytes (ie, neutrophils, basophils, monocytes, and lymphocytes). In addition, with a commercially available sPLA2 activity assay kit, we were able to show high activity of sPLA2 in human eosinophils relative to neutrophils. Investigations at the ultrastructural level showed that sPLA2 in eosinophils is mainly located in specific granules. Immunoelectron microscopy also visualized sPLA2 within phagosomes after addition of opsonized particles to the eosinophils. However, sPLA2 was not detected in the cell-free supernatants of activated eosinophils, in contrast to eosinophil-cationic protein (ECP), which colocalizes with sPLA2 in resting eosinophils. These findings warrant further studies into the role of sPLA2 in eosinophil function.

Cytokine-induced protein tyrosine phosphorylation is essential for cytokine priming of human eosinophils.

BACKGROUND: Human eosinophils are strongly modulated by the eosinophilotrophic cytokines IL-5, IL-3, and granulocyte-macrophage colony-stimulating factor (GM-CSF). A clear intracellular effect of these cytokines is the induction of tyrosine phosphorylation of multiple cellular substrates. However, the relevance of tyrosine phosphorylation for eosinophil functioning has not been established. OBJECTIVE: In this study we have investigated dose-response and time curves of IL-5-, IL-3-, and GM-CSF-induced tyrosine phosphorylation in eosinophils. Moreover, we have evaluated the importance of IL-5-induced tyrosine phosphorylation for priming of human eosinophils. METHODS: Cytokine-induced tyrosine phosphorylation was monitored on western blot with an antiphosphotyrosine antibody (4G10). To probe the relevance of tyrosine phosphorylation for priming, eosinophils were primed with IL-5 in the presence of the tyrosine kinase inhibitor herbimycin A. Platelet activating factor (PAF) was used as a control priming agent. Subsequently, the eosinophils were incubated with serum-treated zymosan (STZ) to activate the respiratory burst. Binding of STZ was determined by FACS analysis. RESULTS: IL-5-, IL-3-, and GM-CSF-induced tyrosine phosphorylation was found at concentrations that primed eosinophil effector mechanism (median effective dose values: approximately 5.10(-11) mol/L, approximately 5.10(-10) mol/L, and approximately 5.10(-12) mol/L for IL-5, IL-3, and GM-CSF, respectively). Cytokine-induced tyrosine phosphorylation was transient with an optimum value at 15 minutes. IL-5 priming of STZ-induced activation of the respiratory burst was blocked by herbimycin A, whereas PAF still primed this response. In fact, herbimycin A inhibited IL-5 priming of STZ binding to human eosinophils. On the other hand, PAF priming of STZ binding was not affected by herbimycin A. Both IL-5-induced and PAF-induced tyrosine phosphorylation were inhibited by herbimycin A. CONCLUSION: These data demonstrate for the first time that IL-5 priming of opsonized particle-induced responses is mediated by tyrosine kinase activity in human eosinophils.

Bactericidal/permeability-increasing protein release in whole blood ex vivo: strong induction by lipopolysaccharide and tumor necrosis factor-alpha.

In this study, the release of bactericidal/permeability-increasing protein (BPI), which is stored in polymorphonuclear leukocytes (PMNL), was analyzed in a whole blood ex vivo system. Of the microbial products tested, lipopolysaccharide (LPS) most potently induced BPI release; FMLP, serum-treated zymosan (STZ), and lipoteichoic acid (LTA) also induced BPI release. In addition, the inflammatory mediator tumor necrosis factor (TNF)-alpha potently activated PMNL in whole blood, via TNF receptor p55, to release BPI, whereas interleukin (IL)-1, IL-8, platelet activating factor, and C5a were poor inducers of BPI release. STZ and phorbol myristate acetate, but not LPS, FMLP, or LTA, stimulated isolated PMNL to release BPI. BPI was released in comparable magnitude with the azurophilic granule protein elastase. Furthermore, both proteins were released with similar kinetics, which started within 30 min after onset of stimulation and lasted 1-4 h.

The effect of salmeterol and nimesulide on chemotaxis and synthesis of PAF and LTC4 by human eosinophils.

Salmeterol is a long-acting beta 2-adrenoceptor agonist, with several antiasthma properties. Nimesulide is a nonsteroidal anti-inflammatory drug, supposed to act by inhibition of phosphodiesterase type IV. This might indicate that the effects of both drugs are mediated by an increase in cyclic adenosine monophosphate (cAMP). For salmeterol, it has been shown that it inhibits the influx of eosinophils into the lungs of guinea-pigs after platelet-activating factor (PAF) challenge, suggesting an effect of cAMP on eosinophil migration. For neutrophils, it has been shown that PAF synthesis is inhibited by cAMP. In the present study, we have, therefore, measured the effect of salmeterol and nimesulide on two important human eosinophil functions: chemotaxis; and synthesis of PAF and leukotriene C4 (LTC4). Both drugs were found to be inhibitors of the chemotactic responses of human eosinophils. However, at comparable concentrations, only nimesulide was able to inhibit the synthesis of PAF and LTC4 in activated eosinophils. These results indicate that although the effects of both drugs are thought to be mediated by an increase in cyclic adenosine monophosphate, they have differential effects on eosinophil chemotaxis and synthesis of lipid mediators.

Inhibition of the production of platelet activating factor and of leukotriene B4 in activated neutrophils by nimesulide due to an elevation of intracellular cyclic adenosine monophosphate.

Nimesulide (CAS 51803-78-2) has been shown to exert a marked anti-inflammatory effect in several in vivo models of inflammation. Recent studies indicate that nimesulide not only inhibits prostaglandin synthesis in certain cell types, but also has pleiotropic effects on neutrophil functions, including the respiratory burst, integrin-mediated adherence and synthesis of platelet-activating factor (PAF). In the present study, the effect of nimesulide on PAF synthesis was compared with its effect on the production of leukotriene B4 (LTB4). Nimesulide dose-dependently inhibited both processes in neutrophils stimulated by serum-treated zymosan (STZ) with a comparable efficacy (IC50 values between 10 and 20 mumol/l). In formyl-methionyl-leucyl-phenylalanine-stimulated neutrophils (treated with cytochalasin B), these IC50 values were 30 and 50 mumol/l for PAF and LTB4 synthesis, respectively. These results indicate an inhibition by nimesulide of a common step in the release of these lipid mediators, i.e. the activation of phospholipase A2, possibly by elevating intracellular cAMP. In support of this latter hypothesis, it was observed that nimesulide increased the level of cAMP almost 3-fold after STZ stimulation, whereas in fMLP-stimulated neutrophils these changes in cAMP levels were more dramatic. Furthermore, the inhibitory effects of nimesulide on PAF and LTB4 production could largely be prevented by addition of H89, an inhibitor of cAMP-dependent protein kinase (PK-A). It is concluded that an increase in intracellular cAMP is instrumental in the observed effects of nimesulide on the release of PAF and LTB4 by activated neutrophils and that limited availability of arachidonic acid, also the substrate for the cyclooxygenase pathway, may very well contribute to the effects of nimesulide on prostaglandin synthesis observed in other cell types.

Eosinophils isolated with two different methods show different characteristics of activation.

Eosinophils can be isolated from a mixed suspension of granulocytes by different procedures. We compared functional responses of human eosinophils purified according to two different principles: (1) an fMLP-induced difference in specific gravity between eosinophils and neutrophils and (2) selective removal of neutrophils by means of immunomagnetic beads coated with CD16 mAb. The results showed that eosinophils isolated with the CD16 beads method have a higher capacity to synthesize platelet activating factor (PAF) after stimulation with serum-treated zymosan (STZ) than eosinophils purified with the fMLP method. Binding of STZ and subsequent activation of the respiratory burst were also increased in CD16-isolated eosinophils. Furthermore, eosinophils isolated with the CD16 beads showed stronger chemotactic responses towards C5a and PAF. The difference in activity of these eosinophil preparations might be explained by a loss of the more active cells during the isolation with the fMLP method: only 30-60% of the eosinophils were recovered with this method, in contrast to a recovery of more than 95% with the CD16 beads method. Indeed, this 'lost' population of eosinophils, subsequently purified with CD16-coated beads, had a higher respiratory burst activity. The alternative explanation, i.e., an enhancement of eosinophil function by the beads method, appeared not to be valid, because repurification of fMLP-isolated eosinophils in the presence of fresh neutrophils and CD16-coated beads did not change the reactivity of the eosinophils. We conclude that the fMLP method leads to selective purification of eosinophils with a resting (or 'unprimed') phenotype.

Granulocyte-macrophage colony-stimulating factor, interleukin-3 (IL-3), and IL-5 greatly enhance the interaction of human eosinophils with opsonized particles by changing the affinity of complement receptor type 3.

Eosinophil functions can be modulated by several cytokines such as granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and IL-5. We have investigated the modulatory role of these cytokines on the interaction of human eosinophils with opsonized particles (serum-treated zymosan [STZ]). Addition of STZ to eosinophils isolated from the peripheral blood of normal human donors resulted in an interaction of the STZ particles with only 15% to 25% of the cells. Treatment of the eosinophils with GM-CSF, IL-3, or IL-5 strongly enhanced both the rate of particle binding and the percentage of eosinophils binding STZ. The effect of the cytokines is most likely mediated by a change in affinity of the complement receptor type 3 (CR3) on the eosinophils for the complement fragment iC3b on the STZ particles. This is indicated by the observation that (1) the effect of the cytokines on STZ binding was prevented by a monoclonal antibody against the iC3b-binding site on CR3 and (2) the enhanced binding was already apparent before upregulation of CR3 on the cell surface was observed. In a previous study, similar results were obtained with platelet-activating factor (PAF)-primed eosinophils. Because we found that the cytokines strongly enhanced the STZ-induced PAF synthesis, we investigated the role of both released PAF and cell-associated PAF in the priming phenomenon by the cytokines. Cytokine priming appeared to be largely independent of the synthesis of PAF.

Phosphatidyl-inositol-linked CD14 is involved in priming of human neutrophils by lipopolysaccharide (LPS), but not in the inactivation of LPS.

The results concerning LPS priming and inactivation are summarized in table 4. This table clearly shows that priming by and inactivation of LPS are mediated via different pathways, because there is no correlation whatsoever between priming and inactivation. LPS priming nicely correlates with CD14 expression. Monocytes express high levels of CD14, and are highly sensitive to LPS. Neutrophils express lower levels of CD14, and also require a higher concentration of LPS to obtain a primed state. Eosinophils express even lower levels of CD14 (if any), and these cells are not primed by LPS up to 150 ng/ml in the presence of serum (data not shown). [table: see text] The inactivation experiments were performed with LPS, but unpublished results from M. Pabst et al. show the same phenomenon with synthetic lipid A. This indicates that the inactivation of LPS is caused by a modification of the lipid A moiety of LPS. As a first step, we tested the hypothesis that the inactivation of LPS is a dephosphorylation of lipid A by alkaline phosphatase (AP). However, AP activity in isolated neutrophils of one of the PNH patients was completely undetectable. Nevertheless, these neutrophils were able to inactivate LPS. This result clearly shows that AP is not the enzyme that inactivates LPS. Secondly, we measured neutral pH 7 phosphatase both in whole cells, and in cell lysate. All cell types tested (neutrophils, eosinophils and monocytes) contained comparable levels of pH 7 phosphatase, but only neutrophils were able to inactivate LPS.(ABSTRACT TRUNCATED AT 250 WORDS)

A novel specificity of anticytoplasmic autoantibodies directed against eosinophil peroxidase.

Vasculitis associated anticytoplasmic autoantibodies (ANCA) are directed against enzymes in the granules of both neutrophils and monocytes. These autoantibodies can be detected by indirect immunofluorescence technique (IIFT) using ethanol-fixed cytospins. We here report the identification of a novel specificity of autoantibodies, present in the sera of eight patients, that reacted only with eosinophils in the IIFT. By immunoprecipitation and ELISA experiments it was shown that the autoantibodies in these sera were directed against eosinophil peroxidase (EPO). There was no apparent influence on initial substrate conversion rate, but reduced plateau levels suggested increased inactivation of the enzyme in the course of the peroxidase reaction. Flow cytometry studies demonstrated the presence of EPO on the surface of primed eosinophils. Anti-EPO sera and purified anti-EPO immunoglobulins significantly increased the release of reactive oxygen species from primed eosinophils. The patients with anti-EPO antibodies suffered from clinically diverse disorders, with more or less generalized manifestations involving the kidneys, blood vessels, lungs and/or joints.

Nimesulide inhibits platelet-activating factor synthesis in activated human neutrophils.

In an inflammatory locus, products of activated neutrophils may be toxic both to the micro-organisms to be eliminated and to the surrounding tissue. In several models of inflammation, nimesulide possesses marked anti-inflammatory properties. The present study was undertaken to further investigate the effects of nimesulide on the activation of human neutrophils. Nimesulide caused a concentration-dependent inhibition of the homotypic aggregation of neutrophils upon activation with the receptor agonist formyl-Met-Leu-Phe. Likewise, nimesulide inhibited the heterotypic interaction of human neutrophils with endothelial cells in suspension. Since both these responses are mediated through activation of the integrin CD11b/CD18 on the neutrophil surface, we conclude that nimesulide interferes with the signal transduction leading to this activation. We also observed a strong inhibition of platelet-activating factor (PAF) synthesis by activated neutrophils in the presence of nimesulide. PAF has been implicated as an intercellular messenger in the diapedesis of neutrophils across endothelial cell monolayers after treatment with cytokines and in the activation of eosinophils.

Priming of human eosinophils by platelet-activating factor enhances the number of cells able to bind and respond to opsonized particles.

Addition of platelet-activating factor (PAF) to human eosinophils leads to the modulation of eosinophil responses. Earlier work from our laboratory has shown that the respiratory burst and homotypic aggregation response in these cells induced by opsonized particles (serum-treated zymosan, STZ), is strongly enhanced after pretreatment (priming) with PAF. In the present study we have investigated the effect of PAF on the binding of fluorescent STZ particles to human eosinophils. Addition of STZ to eosinophils isolated from the peripheral blood of normal donors results in an interaction of the STZ particles with only 30 to 40% of the cells. Treatment of the eosinophils with PAF (1 microM) for 2 min strongly enhanced the rate of particle binding and also doubled the percentage of eosinophils binding STZ. The effect of PAF priming is most likely mediated by a change in CR3, because it is reversed by mAb B2.12 blocking the iC3b binding site of CR3 and unaffected by mAb IV.3 blocking Fc gamma RII. This change is not an increase in cell surface expression of CR3, and it requires an active cellular metabolism to be maintained. The functional consequences of the effect of PAF on STZ binding were investigated in the nitro-blue tetrazolium dye slide test. PAF priming strongly enhanced the percentage of eosinophils producing oxygen radicals after STZ stimulation. Our findings indicate that the priming phenomenon observed in human eosinophils consists, at least in part, of a recruitment of cells able to interact with and to respond to opsonized particles.

Release of platelet-activating factor is important for the respiratory burst induced in human eosinophils by opsonized particles.

The respiratory burst induced in human eosinophils by serum-treated zymosan (STZ) was found to be almost completely prevented by preincubation of the cells with WEB 2086, an antagonist of platelet-activating factor (PAF). When eosinophils were primed by the addition of 1 mumol/L PAF, subsequent addition of WEB 2086 had only a minor effect on the STZ-induced respiratory burst. These results suggest a role for PAF synthesis and PAF release in the activation of the respiratory burst by STZ. Indeed, supernatant of STZ-stimulated eosinophils was able to prime fresh eosinophils (as did PAF itself), and this effect was again inhibited by WEB 2086. This indicates that eosinophils synthesize and release PAF during STZ stimulation. Measurements of total PAF and PAF release showed that most of the PAF synthesized by eosinophils was released in the extracellular medium. This study shows that synthesis and release of PAF is important for respiratory burst activity induced in human eosinophils by STZ.